Charged particle beam devices can be used, for example, in electron beam inspection (EBI), defect review and critical dimension measurement. Upon irradiation of a specimen or sample by a primary charged particle beam, signal charged particles, such as secondary electrons (SE) or backscattered charged particles, are created, which may carry information about the topography of the specimen, the chemical constituents of the specimen, the electrostatic potential of the specimen and other information about the specimen. The signal charged particles are collected and guided to a sensor, e.g., a scintillator, a pin diode or the like.
The performance of a charged particle source, such as an electron emitter, in providing the primary charged particle beam in a charged particle beam device is of particular interest. As an example, high brightness charged particle sources and/or high emission current sources with high emission stability are beneficial. The charged particle sources are operated under vacuum conditions, wherein the performance of the charged particle sources can be related to a quality of the vacuum.
As features on the specimen become smaller, the demands on the resolution and throughput of a charged particle beam device increase. One example of limitations to the throughput is the charged particle source (such as an emitter) and the ability of the charged particle source to deliver current high enough for a small focused spot (high brightness). Known systems use so called Schottky sources (standard or shelf product). Inherent limitations of the known sources originate from the operation principles. Theoretically, a higher brightness can be achieved by a source based on cold field emission and a tunneling effect through the potential barrier on the usually metallic specimen surface. Cold-field emitters do not use high temperatures for operation and the brightness is higher. However, cold field emitter sources are very sensitive to the environmental effect, especially residual gas molecules bombardment, and the emission is often not stable.
In view of the above, it is beneficial to provide an emitter for a charged particle beam, a charged particle beam device, and a method for producing and operating an emitter for a charged particle beam device that overcome at least some of the problems in the art.